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Register a new userA panchromatic spatially-resolved analysis of nearby galaxies -- I. Sub-kpc scale Main Sequence in grand-design spirals
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Added by
Andrea Francesco Maria Enia
Publication date
2020
fields
Physics
and research's language is
English
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We analyse the spatially resolved relation between stellar mass (M$_{star}$) and star formation rate (SFR) in disk galaxies (i.e. the Main Sequence, MS). The studied sample includes eight nearby face-on grand-design spirals, e.g. the descendant of high-redshift, rotationally-supported star-forming galaxies. We exploit photometric information over 23 bands, from the UV to the far-IR, from the publicly available DustPedia database to build spatially resolved maps of stellar mass and star formation rates on sub-galactic scales of 0.5-1.5 kpc, by performing a spectral energy distribution fitting procedure that accounts for both the observed and the obscured star formation processes, over a wide range of internal galaxy environments (bulges, spiral arms, outskirts). With more than 30 thousands physical cells, we have derived a definition of the local spatially resolved MS per unit area for disks, $log(Sigma_{SFR})$=0.82log$(Sigma_{*})$-8.69. This is consistent with the bulk of recent results based on optical IFU, using the H$alpha$ line emission as a SFR tracer. Our work extends the analysis at lower sensitivities in both M$_{star}$ and SFR surface densities, up to a factor $sim$ 10. The self consistency of the MS relation over different spatial scales, from sub-galactic to galactic, as well as with a rescaled correlation obtained for high redshift galaxies, clearly proves its universality.
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In the second work of this series, we analyse the connection between the availability of gas and the position of a region with respect to the spatially resolved main sequence (MS) relation. Following the procedure presented in Paper I we obtain 500pc scales estimates of stellar mass and star formation rate surface densities ($Sigma_{star}$ and $Sigma_{rm{SFR}}$). Our sample consists of five face-on, grand design spiral galaxies located on the MS. Thanks to HI 21cm and $^{12}$CO(2-1) maps, we connect the gas surface densities and gas fractions to the observed star formation properties of each region. We find that the spatially resolved MS ($sigma=0.23$ dex) is the combination of two relations: the Kennicutt-Schmidt law ($sigma=0.19$ dex) and the molecular gas MS (MGMS, $sigma=0.22$ dex); $Sigma_{star}$, $Sigma_{rm{SFR}}$ and the surface density of the molecular gas, $Sigma_{rm{H_2}}$, define a 3D relation as proposed by citet{2019ApJ...884L..33L}. We find that $Sigma_{rm{H_2}}$ steadily increases along the MS relation, varies little towards higher $Sigma_{rm{SFR}}$ at fixed stellar surface densities (not enough to sustain the change in SFR), and it is almost constant perpendicular to the relation. The surface density of neutral gas ($Sigma_{rm{HI}}$) is constant along the MS, and increases in its upper envelop. $Sigma_{rm{SFR}}$ can be expressed as a function of $Sigma_{star}$ and $Sigma_{rm{HI}}$, following the Equation: $logSigma_{rm{SFR}}$ = 0.97$logSigma_{star}$ + 1.99$logSigma_{rm{HI}}$ - 11.11. Finally, we show that f$_{rm{gas}}$ increases significantly towards the starburst region in the $logSigma_{star}$ - $logSigma_{rm{SFR}}$ plane, accompanied by a slight increase in SFE.
We present spatially resolved BPT mapping of the extended narrow line regions (ENLRs) of seven nearby Seyfert 2 galaxies, using HST narrow band filter imaging. We construct the BPT diagrams using $leq$ 0.1 resolution emission line images of [O III]$lambda$5007, H$alpha$, [S II]$lambda$$lambda$6717,6731, and H$beta$. By mapping these diagnostic lines according to the BPT classification, we dissect the ENLR into Seyfert, LINER, and star-forming regions. The nucleus and ionization cones are dominated by Seyfert-type emission, which can be interpreted as predominantly photoionization by the active galactic nucleus (AGN). The Seyfert nucleus and ionization cones transition to and are surrounded by a LINER cocoon, extending up to $sim$ 250 pc in thickness. The ubiquity of the LINER cocoon in Seyfert 2 galaxies suggests that the circumnuclear regions are not necessarily Seyfert-type, and LINER activity plays an important role in Seyfert 2 galaxies. We demonstrate that spatially resolved diagnostics are crucial to understanding the excitation mechanisms in different regions and the AGN-host galaxy interactions.
We use an N-body simulation to study the 3-D density distribution of spirals, and the resulting stellar vertical velocities. Relative to the discs rotation, the phase of the spirals peak density away from the mid-plane trails that at the mid-plane. In addition, at fixed radius the density distribution is azimuthally skewed, having a shallower slope on the trailing side inside corotation and switching to shallower on the leading side beyond corotation. The spirals induce non-zero average vertical velocities, <V_z>, as large as <V_z> ~ 10-20 km/s, consistent with recent observations in the Milky Way. The vertical motions are compressive (towards the mid-plane) as stars enter the spiral, and expanding (away from the mid-plane) as they leave it. Since stars enter the spiral on the leading side outside corotation and on the trailing side within corotation, the relative phase of the expanding and compressive motions switches sides at corotation. Moreover, because stars always enter the spiral on the shallow density gradient side and exit on the steeper side, the expanding motions are larger than the compressing motions.
We present our study on the spatially resolved H_alpha and M_star relation for 536 star-forming and 424 quiescent galaxies taken from the MaNGA survey. We show that the star formation rate surface density (Sigma_SFR), derived based on the H_alpha emissions, is strongly correlated with the M_star surface density (Sigma_star) on kpc scales for star- forming galaxies and can be directly connected to the global star-forming sequence. This suggests that the global main sequence may be a consequence of a more fundamental relation on small scales. On the other hand, our result suggests that about 20% of quiescent galaxies in our sample still have star formation activities in the outer region with lower SSFR than typical star-forming galaxies. Meanwhile, we also find a tight correlation between Sigma_H_alpha and Sigma_star for LI(N)ER regions, named the resolved LI(N)ER sequence, in quiescent galaxies, which is consistent with the scenario that LI(N)ER emissions are primarily powered by the hot, evolved stars as suggested in the literature.
We map optical and near-infrared (NIR) stellar population properties of the inner 320$times$535pc$^2$ of the elliptical galaxy NGC1052. The optical and NIR spectra were obtained using the Gemini Integral Field Units of the GMOS instrument and NIFS, respectively. By performing stellar population synthesis in the optical alone, we find that this region of the galaxy is dominated by old (t$>$10Gyr) stellar populations. Using the NIR, we find the nucleus to be dominated by old stellar populations, and a circumnuclear ring with younger ($sim$2.5Gyr) stars. We also combined the optical and NIR datacubes and performed a panchromatic spatially resolved stellar population synthesis, which resulted in a dominance of older stellar populations, in agreement with optical results. We argue that the technique of combining optical and NIR data might be useful to isolate the contribution of stellar population ages with strong NIR absorption bands. We also derive the stellar kinematics and find that the stellar motions are dominated by a high ($sim$240km$cdot$s$^{-1}$) velocity dispersion in the nucleus, with stars also rotating around the center. Lastly, we measure the absorption bands, both in the optical and in the NIR, and find a nuclear drop in their equivalent widths. The favored explanation for this drop is a featureless continuum emission from the low luminosity active galactic nucleus.
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